Plants are constantly exposed to a variety of biotic (i.e., pathogen infection and insect herbivory) and abiotic (i.e., high or low temperature, drought, and salinity) stresses. To survive these challenges, plants have developed elaborate mechanisms to perceive external signals and to manifest adaptive responses with proper physiological and morphological changes (Bohnert et al., 1995). Plants exposed to low water or drought conditions typically have low yields of plant material, seeds, fruit and other edible products. Some countries of the world consistently have very low rainfall and therefore have problems growing sufficient food crops for their population. Yet it has been observed that some plants survive and thrive in low water environments. It would, therefore, be of great interest and importance to be able to identify genes that confer improved water efficiency characteristics to thereby enable one to create transformed plants (such as crop plants) with improved water efficiency characteristics to, thereby better survive low water and drought conditions.
Exogenous application of high concentrations of PEG and/or mannitol to plants is known to produce osmotic stress resulting in the retardation of growth and vigor and is used to assess drought responses. Exogenous application of ABA stimulates drought-responses in plants and can, therefore also be an important screen to identify genes that confer improved water efficiency.
In the field of agriculture and forestry efforts are constantly being made to produce plants with an increased growth potential in order to feed the ever-increasing world population and to guarantee the supply of reproducible raw materials. This is done conventionally through plant breeding. The breeding process is, however, both time-consuming and labor-intensive. Furthermore, appropriate breeding programs must be performed for each relevant plant species.
Progress has been made in part by the genetic manipulation of plants; that is by introducing and expressing recombinant nucleic acid molecules in plants. Such approaches have the advantage of not usually being limited to one plant species, but instead being transferable among plant species. For example, EP-A 0 511 979 describes the expression of a prokaryotic asparagine synthetase gene in plant cells that leads to increased biomass production. Likewise, WO 96/21737 describes plants with increased yield (growth potential) arising from an increase in the photosynthesis rate and the expression of deregulated or unregulated fructose-1,6-bisphosphatase. Nevertheless, there still is a need for generally applicable processes that improve forest or agricultural plant growth potential. Therefore, the present invention relates to a process for increasing the growth potential in plants, characterized by expression of the recombinant DNA molecules of the invention stably integrated into the plant genome.